This proposal requests continued support for a program of basic and clinical research on children with profound hearing impairments. The long-term goal of this project is to obtain a better understanding of the benefits derived from multichannel cochlear implants (CIs) and conventional amplification (HA). In particular, we are interested in the effects of cochlear implants on the development of speech perception, spoken word recognition, and receptive language skills. The proposed research is organized into three projects. First, we propose to examine the effects of age at implantation on speech and language development in a group of children who are all implanted prior to age five years. Second, we plan to compare the performance of children with CIs to children with HAs, to assess the benefits obtained from CIs by children with different degrees of hearing loss. Third, we propose to investigate individual differences and variation in the effectiveness of CIs using new cognitive measures of working memory and learning. Taken together the findings from this project will provide new information concerning audiological criteria for CI candidacy and the underlying sensor, perceptual and cognitive basis for individual differences in spoken word recognition and receptive language outcome measures. Understanding the nature of the wide individual differences to the effectiveness of CIs in young children is critical for predicting individual benefits prior to surgery and selecting appropriate intervention strategies following implantation.